Looking to upgrade my XPS3800

Hey,

So I've had this computer for quite the time now and I was looking to boost the graphics card mostly but also wanting to know if there is anything else i can do to make it better. I'm pretty inexperienced when it comes to messing with hardware but I've noticed now a lot of games i want to play require better graphics cards. If you guys could help me and give me some ideas that would be great! I'm trying to keep on a rather low price though. 

Motherboard: Dell Inc. 0Y2MRG

Graphics Card: ATI Radeon HD 5670 

RAM: 6127 MB

Power Supply: 460W

CPU: Processor Intel(R) Core(TM) i5-2400 CPU 

CPU Speed: 3147.1 MHz